Transseptal crossing system for single pass large bore access

ABSTRACT

A single pass, large bore transseptal crossing catheter system is disclosed. An elongate, flexible tubular body has a proximal end, a distal end and an electrically conductive sidewall defining a central lumen. An insulation layer surrounds the sidewall and leaves exposed a first distal electrode tip. An inner conductive wire is provided, having a second distal electrode tip. The inner wire is axially movably extendable through the central lumen. A tubular insulation layer is provided in between the wire and the electrically conductive sidewall.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit under 35 U.S.C. § 119(e) ofU.S. Provisional Application No. 63/024,986, filed May 14, 2020, theentirety of which is hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

Transseptal crossing is used to access the left atrium crossing from theright atrium through the septal wall for any of a variety of EP orstructural heart procedures. For example, the left atrium is routinelyaccessed to assess hemodynamics and/or perform mitral valvuloplasty, orto accommodate transvascular atrial fibrillation (AF) ablationprocedures.

Crossing the septum normally requires locating and puncturing the fossaovalis to access the left atrium. Locating the fossa ovalis may beaccomplished using fluoroscopy and ultrasound, and potentiallyechocardiography.

Mechanical puncture through the tissue of the fossa ovalis can beaccomplished using a piercing tool such as a standard Brockenbroughneedle as is understood in the art. Alternatively, a transseptal needlehaving a radio frequency energized tip may be used, such as thoseproduced by Baylis Medical Company, Inc.

The foregoing devices and techniques have proven useful in a variety ofEP and structural heart procedures, in which the procedural accesssheath is often no larger than about 11 French. However, a growingnumber of procedures such as left atrial appendage occlusion deviceimplantation and various Mitral valve replacement or repair require“large bore” access, which is not possible using the above techniquesalone.

Instead, traditional transseptal puncture is normally carried out withsmall bore sheaths ranging from 8 Fr to 11 Fr which are then exchangedover stiff guidewires for the large bore sheaths with outer dimensionsas large as 24 Fr in the case of the MitraClip Steerable Guide Catheter.Dilators for the transseptal sheaths usually accommodate 0.032 wires,however Baylis has introduced a small bore transseptal sheath with adilator that accommodates a 0.035 wire. Regardless of the transseptalsheath, the operator must utilize a number of additional pieces ofequipment including the small bore transseptal sheath and dilator, andoften a 0.025 “stiff” pigtail wire (Baylis, Toray) to use as a rail todrive the small bore transseptal sheath and dilator before switching toa 0.035 guidewire (Amplatz extra stiff or Safari) to drive the largebore sheath safely into the LA. The entire small bore sheath must bedriven into the LA to make the switch to the appropriate stiff 0.035guidewire to drive the large bore sheath.

Thus, there remains a need for a transseptal crossing system that isbased upon a 0.035 inch guidewire access, that enables single passcrossing of larger sheaths, such as the Boston Scientific Watchman guidesheath, Medtronic Flexcath and others known in the art or yet to bereleased.

SUMMARY OF THE INVENTION

In general, the present invention provides a single pass transseptalcrossing device, for enabling large bore access in a single pass. Thesystem includes an insulated cannula with a conductive tip positionablethrough the dilator of a large bore sheath. The tip of the cannula isexpressed distal to the tip of the dilator. The insulated cannula canserve as an electrical conduit of RF energy. The cannula can beenergized to deliver RF energy directly to tissues and/or through aseparate conductive wire or obturator. An insulated wire or obturatorcan thus be independently energized or can be energized passively viathe energized cannula. The cannula may be 0.050″ OD and approximately0.038″ ID allowing delivery of a 0.035″ wire which together (stiff 0.035wire and 0.050 cannula) creates a sturdy rail to drive large boredilators and sheaths in a single pass. The tip of the cannula can bescalloped to deliver high density current to the scalloped edges forimproved cutting. The system permits irrigation with hypotonic saline orD5W to preferentially drive current through the myocardium.

Thus, there is provided in accordance with one aspect of the presentinvention a single pass, large bore transseptal crossing catheter, suchas for accessing the left atrium of the heart. The catheter comprises anelongate, flexible tubular body, having a proximal end, a distal end andan electrically conductive sidewall defining a central lumen. Aninsulation layer surrounds the sidewall and leaving exposed a firstdistal electrode tip. An inner conductive wire having a second distalelectrode tip, is axially movably extendable through the central lumen.A tubular insulation layer is provided in between the wire and theelectrically conductive sidewall.

The first distal electrode tip may comprise an annular conductivesurface at the distal end of the tubular body. The second distalelectrode tip may be concentrically extendable through the annularconductive surface. The first distal electrode tip may comprise at leastone distal projection, or at least two or three projections and in oneimplementation comprises a scalloped distal edge.

The second distal electrode may comprise a smooth, hemisphericalsurface, or may be provided with a sharpened distally facing projection.The catheter may additionally comprise an annular lumen extendingbetween the tubular body and the wire, from the proximal hub to an exitport at the distal end.

In accordance with a further aspect of the present invention, there isprovided an introducer sheath, for enabling a single pass, large boretransseptal crossing. The introducer sheath comprises an elongate,flexible tubular body, having a proximal end, a distal end and anelectrically conductive sidewall defining a central lumen. A tubularinsulation layer may surround the sidewall, leaving exposed an annularconductive surface at the distal end. A proximal hub may be provided onthe tubular body, having at least one access port in communication withthe central lumen. A connector may be carried by the proximal end, inelectrical communication with the conductive sidewall. The distalconductive surface may comprise at least one distal projection, or atleast two or three projections and in one implementation comprises ascalloped distal edge.

There is also provided a method of accessing the left atrium with alarge bore catheter in a single pass. The method comprises providing asingle pass, large bore transseptal crossing catheter; positioning thedistal end in contact with a fossa ovalis; and energizing the distal endto enable passage of the distal end into the left atrium.

The energizing step may comprise energizing a first distal electrode tipon a conductive tubular cannula and/or energizing a second distalelectrode tip on an RF core wire. The first and second distal electrodetips may be energized in a bipolar mode.

The method may comprise accessing the left atrium, energizing the seconddistal electrode tip, advancing the wire through the fossa ovalis,thereafter energizing the first distal electrode tip and advancing thecannula into the left atrium.

A large bore access sheath may thereafter be advanced over thetransseptal crossing catheter and into the left atrium, and thetransseptal crossing catheter may then be removed, leaving the largebore access sheath extending into the left atrium.

An index procedure catheter may be advanced through the large boreaccess sheath and into the left atrium. The index procedure catheter maybe configured to deliver a left atrial appendage implant such as anocclusion device, or to accomplish a mitral valve repair or replacement.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a transseptal crossing system inaccordance with the present invention.

FIG. 2 is a side elevational view of an RF needle in accordance with thepresent invention.

FIG. 2A is a cross section taken along the line A-A in FIG. 2.

FIG. 2B is a detail view of the distal tip of the needle in FIG. 2.

FIG. 3 is a cross sectional view through the needle of FIG. 2.

FIG. 4A-4C are detail views of the distal energy delivery tip of oneimplementation of the invention.

FIG. 5A-5C are detail views of the distal energy delivery tip of anotherimplementation of the invention.

FIG. 6 is a schematic cross section of a portion of a human heart,having a transseptal crossing system of the present invention positionedin the right atrium.

FIG. 7 is a view as in FIG. 6, showing positioning of the distal tip ofthe transseptal crossing system at the fossa ovalis.

FIG. 8 shows penetration of the guidewire and cannula through the fossaovalis.

FIG. 9 shows penetration of the large bore sheath and dilator crossingthe fossa ovalis.

FIG. 10 shows the large bore sheath in position across the septum withthe dilator and other system components removed to provide access to theleft atrium.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates an embodiment of a tissue penetrating apparatus 102in a transseptal crossing system 100. Apparatus 102 comprises anelongate tubular body 104 having a distal region 106, and a proximalregion 108. Distal region 106 is adapted to be inserted within and alonga lumen of a body of a patient, such as a patient's vasculature, andmaneuverable therethrough to a desired location proximate material, suchas tissue, to be perforated.

In some embodiments, the tubular body 104 may have at least one lumenextending from proximal region 108 to distal region 106 such as lumen208 shown in FIG. 2A. Tubular body 104 may be constructed of abiocompatible polymer material jacket typically with a metal core thatprovides column strength to apparatus 102. The tubular body 104 issufficiently stiff to permit a dilator 84 and a large bore guidingsheath 12 (See FIG.6) to be easily advanced over apparatus 102 andthrough a perforation. Examples of suitable materials for the tubularportion of tubular body 104 are stainless steel, nitinol,polyetheretherketone (PEEK), nylon, and polyimide. In the illustratedembodiment, the outer diameter along the tubular portion of tubular body104 may taper down to distal region 106. In alternate embodiments, theouter diameter along tubular body 104 remains substantially constantfrom proximal region 108 to distal region 106.

Distal region 106 comprises a softer polymer material with an optionalembedded braid or coil so that it is pliable and atraumatic whenadvanced through vasculature. In some embodiments, the material is alsoformable (e.g., Nitinol or stainless steel with a polymer jacket), sothat its shape can be changed during manufacturing, typically byexposing it to heat while it is fixed in a desired shape. In analternate embodiment, the shape of distal region is modifiable by theoperator during use. An example of a suitable plastic is PEBAX (aregistered trademark of Atofina Chemicals, Inc.). In the presentembodiment, the distal region 106 comprises a curve portion 115.

As the distal region 106 is advanced out of a guiding sheath, it mayhave a preset curve so that it curls away from the general axis of thesheath which helps ensure that energy delivery tip 112 is not in aposition to inadvertently injure unwanted areas within a patient's heartafter trans-septal perforation. Curve length may be about 4 cm (about1.57″) to about 6 cm (about 2.36″) and the curve may traverse about 225to about 315 degrees of the circumference of a circle. For example, thecurve may be about 5 cm in length and may traverse about 270 degrees ofthe circumference of a circle. Such an embodiment may be useful to avoidunwanted damage to cardiac structures.

In some embodiments, curve portion 115 begins about 0.5 cm to about 1.5cm proximal to energy delivery device 112, leaving an approximately 1 cm(about 0.39″) straight portion in the distal region 106 of apparatus102. This ensures that this initial portion of apparatus 102 will exitdilator 84 (see FIG. 6) without curving, enabling the operator to easilyposition the apparatus 102, for example, against a septum as describedfurther below. This feature further ensures that the distal region 106of apparatus 102 will not begin curving within the atrial septum.

Distal region 106 may have a smaller outer diameter compared to theremainder of tubular body 104 so that dilation of a perforation islimited while the distal region 106 is advanced through the perforation.Limiting dilation seeks to ensures that the perforation will not causehemodynamic instability once apparatus 102 is removed. In someembodiments, the outer diameter of distal region 106 may be no largerthan about 0.8 mm to about 1.0 mm. For example, the outer diameter ofdistal region 106 may be about 0.9 mm (about 0.035″). This is comparableto the distal outer diameter of the trans-septal needle that istraditionally used for creating a perforation in the atrial septum.Similarly, in some embodiments, the outer diameter of tubular body 104may be no larger than about 0.040″ to about 0.060″. For example, theouter diameter of tubular body 104 may be about 0.050″ (1.282 mm), whichis also comparable to the trans-septal needle dimensions.

Distal region 106 terminates at functional tip region 110, whichcomprises an energy delivery component and optionally also as an ECGmeasuring device. Functional tip region 110 comprises at least oneenergy delivery tip 112 made of a conductive and optionally radiopaquematerial, such as stainless steel, tungsten, platinum, or another metal.One or more radiopaque markings may be affixed to tubular body 104 tohighlight the location of the transition from distal region 106 to theremainder of tubular body 104, or other important landmarks on apparatus102. Alternately, the entire distal region 106 of apparatus 102 may beradiopaque. This can be achieved by filling the polymer material, forexample PEBAX, used to construct distal region 106 with radiopaquefiller. An example of suitable radiopaque filler is Bismuth. Distalregion 106 may contain at least one opening 109 which is in fluidcommunication with main lumen 200 (FIG. 2A) as described further below.

In the illustrated embodiment, proximal region 108 comprises a hub 114,to which are attached a catheter connector cable 116, and connector 118.Tubing 117 and adapter 119 are attached to hub 114 as well. Proximalregion 108 may also have one or more depth markings 113 to indicatedistances from functional tip region 110, or other important landmarkson apparatus 102. Hub 114 comprises a curve direction or orientationindicator 111 that is located on the same side of apparatus 102 as thecurve 115 in order to indicate the direction of curve 115. Orientationindicator 111 may comprise inks, etching, or other materials thatenhance visualization or tactile sensation. One or more curve directionindicators may be used and they may be of any suitable shape and sizeand a location thereof may be varied about the proximal region 108.

In the illustrated embodiment, adapter 119 is configured to releaseablycouple apparatus 102 to an external pressure transducer 121 via externaltubing 123. External pressure transducer 121 is coupled to a monitoringsystem 125 that converts a pressure signal from external pressuretransducer 121 and displays pressure as a function of time. Catheterconnector cable 116 may connect to an optional Electro-cardiogram (ECG)interface unit via connector 118. An optional ECG connector cableconnects an ECG interface unit to an ECG recorder, which displays andcaptures ECG signals as a function of time. A generator connector cablemay connect the ECG interface unit to an energy source such as agenerator (not illustrated). In this embodiment, the ECG interface unitcan function as a splitter, permitting connection of the electrosurgicaltissue piercing apparatus 102 to both an ECG recorder and generatorsimultaneously. ECG signals can be continuously monitored and recordedand the filtering circuit within the ECG interface unit and may permitenergy, for example RF energy, to be delivered from generator 128through electrosurgical apparatus 102 without compromising the ECGrecorder.

In another embodiment (not shown) of apparatus 102, there may be adeflection control mechanism associated with the distal region 106 ofapparatus 102 and an operating mechanism to operate said controlmechanism associated with the proximal region 108 of apparatus 102. Oneor two or more pull wires may extend from a proximal control to thedistal region 106 to actively deflect the distal region 106 as will beunderstood in the art. The control mechanism may be used to steer orotherwise actuate at least a portion of distal region 106.

Generator 128 may be a radiofrequency (RF) electrical generator that isdesigned to work in a high impedance range. Because of the small size ofenergy delivery tip 112the impedance encountered during RF energyapplication is very high. General electrosurgical generators aretypically not designed to deliver energy in these impedance ranges, soonly certain RF generators can be used with this device. In oneembodiment, the energy is delivered as a continuous wave at a frequencybetween about 400 kHz and about 550 kHz, such as about 460 kHz, avoltage of between 100 to 200 V RMS and a duration of up to 99 seconds.A grounding pad 130 is coupled to generator 128 for attaching to apatient to provide a return path for the RF energy when generator 128 isoperated in a monopolar mode.

Other embodiments could use pulsed or non-continuous RF energy. Someembodiments for pulsed radio frequency energy have radio frequencyenergy of not more than about 60 watts, a voltage from about 200 Vrms toabout 400 Vrms and a duty cycle of about 5% to about 50% at about fromslightly more than 0 Hz to about 10 Hz. More specific embodimentsinclude radio frequency energy of not more than about 60 watts, avoltage from about 240 Vrms to about 300 Vrms and a duty cycle of 5% to40% at 1 Hz, with possibly, the pulsed radio frequency energy beingdelivered for a maximum of 10 seconds. In one example, the generator canbe set to provide pulsed radio frequency energy of not more than about50 watts, a voltage of about 270 Vrms, and a duty cycle of about 10% at1 Hz. Alternatively, the pulsed radio frequency energy could compriseradio frequency energy of not more than about 50 watts, a voltage ofabout 270 Vrms, and a duty cycle of about 30% at 1 Hz.

In still other embodiments of apparatus 102, different energy sourcesmay be used, such as radiant (e.g. laser), ultrasound, thermal or otherfrequencies of electrical energy (e.g. microwave), with appropriateenergy sources, coupling devices and delivery devices depending upon thedesired clinical performance.

Additional details of the tissue penetration apparatus 102 are describedin connection with FIG. 2. Referring to FIGS. 2 and 2A, the tubular body104 comprises a cannula 206 such as a 0.050″ cannula having a centrallumen 208 extending therethrough. The lumen 208 is dimensioned toslidably receive a guide wire 210 such as an 0.035″ guidewire. Incertain implementations of the invention, it may be desirable toelectrically isolate the guide wire 210 from the cannula 206. This maybe accomplished by providing a tubular insulation layer 212 positionedbetween the guide wire 210 and the cannula 206. In the illustratedembodiment, the insulation layer 212 comprises a coating or tubularsleeve surrounding the guide wire 210. A further tubular insulationlayer 214 may be provided on the outside of the cannula 206 toelectrically isolate the cannula 206 from the patient.

Referring to FIG. 2B, there is illustrated a detail view of the distalend 202 of cannula 206, having a guide wire 210 extending therethrough.The guide wire 210 may comprise a pigtail or other curved distal end asis understood in the art.

Referring to FIG. 3, the tissue penetrating apparatus 102 mayadditionally be provided with a Y connector 220, having a proximal guidewire access port 222 and a flush port 224 in communication with thedistal region 106 such as via exit port 109 (FIG. 1) or cannula 206central lumen 208. The Y connector 220 may be provided with a distalfirst connector 226 configured to cooperate with a second complementaryconnector 228 on the proximal end of the hub 114. First connector 226and second connector 228 may be complementary components of a standardluer connector as is understood in the art. Alternatively, the hub 114and Y connector 220 may be formed as an integral unit.

FIGS. 4A-4C illustrate the axial slidability of the guidewire 210 withinthe cannula 206. In FIG. 4C, the guidewire has been proximally retractedinto the central lumen 208 so that the leading surface of the system isan annular charge transfer surface 207, which comprises a distal endface of the cannula 206. The insulation layer 214 on cannula 206 mayextend distally all the way to the edge of the end face of the cannula206, or to no more than 2 mm or 1 mm or less proximally of the end faceof the cannula 206. The system thus permits delivering RF energy fromeither the guidewire alone, or the cannula alone or both, depending uponthe desired clinical performance.

The separately insulated cannula 206 and guidewire can be configured todeliver bipolar electricity to the distal tip. The cannula 206 can beused as the ground path and replace the body pad or other electrode,which may provide desirable impedance characteristics depending upon thedesired clinical performance.

FIGS. 5A-5C illustrate a modified distal end face of the cannula 206. Atleast one distal extension 220 is carried by the cannula 206, to providea site of enhanced energy density on the leading charge transfer surface207 carried by the projection 220. At least two or four or moreprojections 220 may be provided, such as 10 as illustrated in FIG. 5B,creating scalloped surface with a plurality of circumferentially spacedapart distal transfer surfaces 207.

One method of delivering a large bore catheter in a single pass usingthe transseptal puncture system of the present invention may be asfollows.

-   1. Advance a guidewire (GW) into the superior vena cava (SVC) and    deliver a large bore catheter (e.g., left atrial appendage occlusion    device; mitral valve repair or replacement; intra atrial adjustable    annuloplasty device) with a dilator to the SVC.-   2. Withdraw GW inside of the dilator.-   3. Withdraw the large bore sheath and the dilator down to the right    atrium.-   4. Steer the sheath and dilator into position in the interatrial    septum, specifically tenting the septum with the dilator.-   5. Deliver the cannula and GW into position with the cannula    extending distally beyond the dilator and the GW distally beyond the    cannula and in contact with the fossa ovalis.-   5 a. If necessary for positioning purposes, withdraw cannula    proximal to the bend of the steerable sheath, then step 6.-   6. Activate the distal tip of the GW with RF energy, and pass the GW    through the septum and into the left atrium (LA).-   7. Drive the cannula, dilator and sheath distally through the septum    and into the LA.-   8. If the cannula cannot pass through the septum into the LA,    activate the distal tip of the cannula with RF energy and advance    the cannula into the LA.-   9. Drive the dilator and the large bore sheath over the access    cannula and into the LA.-   10. Withdraw the cannula and dilator, and introduce the index    procedure catheter through the large bore sheath.

As will be appreciated by those of skill in the art, the GW and cannulacan alternatively be simultaneously operated in monopolar mode; eitherthe GW or cannula can be energized separately; or the GW and cannula canbe operated in bipolar mode, depending upon the desired clinicalperformance.

Thus, referring to FIG. 6, there is illustrated a schematiccross-section of a portion of the heart 10. The right atrium 86 is incommunication with the inferior vena cava 88 and the superior vena cava90. The right atrium 86 is separated from the left atrium 16 by theintraatrial septum 18. The fossa ovalis 92 is located on the intraatrialseptum 18. As seen in FIG. 6, a large bore transseptal sheath 12 mayhave a dilator 84, both riding over the cannula 206and guidewire 210,all positioned within the right atrium 86.

The combination of the sheath 12 with the dilator 84 having thetransseptal cannula 206 and GW 210 extending distally therefrom, is thendrawn proximally from the superior vena cava while a curved section ofthe sheath, alone or in combination with a preset curve at the distalregion of dilator 84 and or cannula 206, causes the tip of thecannula-GW combination to “drag” along the wall of the right atrium 86and the septum 18, by proximal traction until the tip pops onto thefossa ovalis 92, as shown in FIG. 7.

After the tip of the cannula-GW combination has been placed in thedesired location against the fossa ovalis 92, RF energy is applied viathe tip of the transseptal GW 210 to allow the GW 210 to pass throughthe septum into the LA. As previously described, RF energy may also bedelivered via the distal end of the cannula 206 if desired. See FIGS. 8and 9.

One medical technique is to confirm the presence of the tip of thetransseptal GW 210 within the left atrium 16. Confirmation of suchlocation of the tip of the transseptal GW 210 may be accomplished bymonitoring the pressure sensed through a transseptal GW lumen or anannular lumen defined between the GW 210 and the inside surface of thecannula 206 central lumen to ensure that the measured pressure is withinthe expected range and has a waveform configuration typical of leftatrial pressure. Alternatively, proper position within the left atrium16 may be confirmed by analysis of oxygen saturation level of the blooddrawn through an available lumen; i.e., aspirating fully oxygenatedblood. Finally, visualization through fluoroscopy alone, or incombination with the use of dye, may also serve to confirm the presenceof the tip of the transseptal cannula 206 and GW 210 in the left atrium16.

After placing the transseptal cannula tip within the left atrium 16, thetip of the dilator 84 is advanced through the septum 18 and into theleft atrium 16, as shown in FIG. 9. When the tapered tip of dilator 84appears to have entered the left atrium 16, the transseptal cannula 206may be withdrawn. The large bore sheath 12 may then be advanced into theleft atrium 16, either by advancing the sheath 12 alone over the dilator84 or by advancing the sheath 12 and dilator 84 in combination. Thedilator 84 may then be withdrawn from sheath 12 when the latter has beenadvanced into the left atrium, thus leaving the main lumen of sheath 12as a clear pathway to advancing further large bore diagnostic ortherapeutic instruments into the left atrium.

What is claimed is:
 1. A single pass, large bore transseptal crossingcatheter system, comprising: an elongate, flexible tubular body, havinga proximal end, a distal end and an electrically conductive sidewalldefining a central lumen; an insulation layer surrounding the sidewalland leaving exposed a first distal electrode tip; an inner conductivewire having a second distal electrode tip, axially movably extendablethrough the central lumen; and a tubular insulation layer in between thewire and the electrically conductive sidewall.
 2. A single pass systemas in claim 1, wherein the first distal electrode tip comprises anannular conductive surface at the distal end of the tubular body.
 3. Asingle pass system as in claim 2, wherein the second distal electrodetip is concentrically extendable through the annular conductive surface.4. A single pass system as in claim 1, wherein the first distalelectrode tip comprises at least one distal projection.
 5. A single passsystem as in claim 1, wherein the first distal electrode tip comprises ascalloped distal surface.
 6. A single pass system as in claim 2, whereinthe second distal electrode comprises a smooth, hemispherical surface.7. A single pass system as in claim 1, further comprising an annularlumen extending between the tubular body and the wire.
 8. A single passsystem as in claim 1, wherein the conductive wire includes a centrallumen.
 9. A single pass system as in claim 1, wherein the sidewallcomprises a stainless steel tube.
 10. A single pass system as in claim1, further comprising an annular conductive surface on the distal end ofthe tubular body.
 11. A single pass system as in claim 4, comprising atleast four distal projections.
 12. A single pass system as in claim 1,wherein the tubular body has an outside diameter of about 0.050 inches.13. A single pass system as in claim 12, wherein the inner conductivewire has an outside diameter of about 0.035 inches.
 14. A single passsystem as in claim 1, having an outside diameter of at least about 0.040inches.
 15. A single pass system as in claim 1, having an outsidediameter of at least about 0.045 inches.
 16. A single pass system as inclaim 1, having sufficient structural integrity to guide a large borecatheter transvascularly through a septal wall and into a left atrium ofthe heart.
 17. A single pass system as in claim 1, which exhibitssufficient structural integrity to guide a large bore cathetertransvascularly through a septal wall and into a left atrium of theheart.
 18. A single pass system as in claim 14, in which no part of theelectrically conductive sidewall is a braided or woven wire.